Imagine if, in addition to sharing photos of those muffins you just baked, you could share their delicious aroma, too. That’s the promise of an AI-assisted device that can transmit smells over the internet. So far, it works on only a small number of scents, including orange, beer and cake, but its creators hope the system will ultimately recreate more smells. The scent of a pine forest or the aroma of coffee, for example, could then add a new dimension to virtual worlds and long-distance communication.

Although it is now routine to communicate sight, sound and even touch sensations electronically, smell is “still a very undeveloped sense”, says at the Ohio State University. That’s partly because odours involve complex chemistry. Whereas vision, for example, can be broken down into combinations of red, green and blue pixels, says Yang, there’s no simple building block underlying smell. Any attempt to convert aromas into electronic signals has to recognise combinations of very different molecules.

To solve the problem, Yang and her colleagues built an electronic nose, or “e-nose”, as well as a smell generator, then used machine learning to connect the two. The e-nose consists of arrays of sensors made of metal oxide. When different gaseous components of smells, such as ethanol (from alcoholic drinks) or limonene (found in citrus fruits), bind to the sensors’ surface, this changes their resistance, creating different electrical signals.

The researchers then trained an AI algorithm to recognise the distinctive signals created by smells from five different foods or beverages: orange, cake, coffee, beer and red wine. Teaching the AI to correctly recognise the smells was “the most challenging part” of the entire study, says Yang, because to generate enough data to train the system, she had to expose the sensors to the various smells hundreds of times.

This information was then sent over the internet to a smell generation device that the researchers are calling “Scentronic”. This part of the system involves miniature containers holding liquids laced with each of the five smells. Above each container is an atomiser that vibrates in response to electric signals, forcing the liquid in the container through a cotton filter and releasing fine droplets into the air, creating the appropriate smell, or combination of smells.

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Yang built several different designs including stringing the atomisers onto a necklace and a wristband, and mounting them on a handheld device. When she tested the handheld device on 14 volunteers, they correctly identified the smells being transmitted to them 73 per cent of the time, on average.

She also built a prototype that reproduces taste, involving a cup of water with electromagnetic pumps containing flavoured liquid fixed around its edge. “When it receives information from the internet, the corresponding liquid will be dropped into the cup.”

Alternative methods to generate smells remotely have been suggested, including to release particular scents, and even to create the experience of smell. But Yang argues her method is both fast and practical. She now hopes to expand the repertoire of the system, to create more complex aromas.

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She suggests the entertainment industry could be first to develop the technology, to create more immersive virtual worlds. But there could also be health applications. For instance, the smell of food transforms the eating experience, so the technology could be adapted to make soldiers’ or astronauts’ rations more palatable. The Scentronic system could also enable doctors to assess distortions in patients’ sense of smell, for example, in post-viral illness or neurodegenerative disease.

The Scentronic system is “a great idea” and a step in the right direction, says at University College London, although she points out that recognising a smell and then releasing a matching one from a limited library is very different from the ease with which we can transmit sound and vision. “There’s still a long way to go before we can truly record and replay smell experiences.”

Leap seconds, previously used to keep the world’s clocks in sync with Earth’s rotation, are to be abolished. Instead, universal time will be allowed to drift up to an hour from astronomical time before it is corrected. Representatives from 69 countries voted for the change on 15 October at a meeting of the in Versailles, France.

As the gap between clock time and astronomical time slowly grows, the effect will eventually be “like living on daylight saving time”, but permanently, says , curator of time at the Royal Observatory in Greenwich, London.

For most of history, our clocks have been set by the apparent position of the sun in the sky. But in 1967, after the development of super-accurate atomic clocks, physicists defined an international time standard called coordinated universal time (UTC), based instead on the speed of a particular vibration of the caesium-133 atom.

Natural fluctuations in Earth’s rate of rotation meant periodic corrections were needed to keep universal time in sync with the sky. As the rotation slowed, physicists added extra leap seconds. Twenty-seven have been added to UTC since they were introduced in 1972.

Now, that strategy is to be abandoned. This is partly because technological systems, from stock markets to telecommunications to GPS, have become much more reliant on precise timekeeping. That means introducing leap seconds is more complex, potentially risking the failure of mobile phone networks or electricity grids. Previous leap seconds have caused websites to crash and disrupted airlines’ booking systems, says at the National Physical Laboratory (NPL) in Teddington, UK.

“Time is now so much more important and integrated into these systems,” says Akkermans. “What once worked has become more problematic.”

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What’s more, Earth’s rotation has recently begun to accelerate slightly, raising the daunting possibility of needing “a first-ever negative leap second”, said , who heads the BIPM’s committee on time and frequency, in a statement. The practical consequences of such a jump backwards in time are hard to predict.

Physicists have been debating what to replace the leap second with for the past 30 years. At the BIPM meeting, they finally voted for a “leap hour”, which means that UTC will be allowed to diverge from astronomical time for up to an hour before being corrected. That should ensure an uninterrupted flow of time for “several centuries”, said Dimarcq. The change will take effect from 20 May 2027.

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Shemar emphasises that the effects involved are very small: “It’ll be many hundreds or even thousands of years before a leap hour is needed.” He adds that physicists will still be accurately tracking Earth’s rotation to provide information for astronomy and celestial navigation.

The leap hour isn’t the only temporal innovation being planned, though. The BIPM meeting also asked for proposals on a new definition of the second – needed because optical clocks are now much more accurate than the caesium clock that time is currently based on – and called on international agencies to start considering how to define a universal time standard for the moon. Overall, the changes “will have a profound impact on future timekeeping both on Earth and other planets”, said Dimarcq.

Microplastics generated potentially harmful molecules when they contacted serum from blood in a lab experiment. This is due to their large surface area enabling such reactions. If this effect occurs within our bodies, it could explain why they have been linked to cell damage and other health concerns.

Several recent studies have linked microplastics, which form when plastics degrade in the environment, to issues such as poor cognition and cardiovascular disease. This seems to be related to the production of destructive molecules called reactive oxygen species, says at Columbia University in New York. These can then react with different molecules inside cells, contributing to issues like inflammation.

But the extent to which common plastics could be causing such problems was unclear. They don’t always contain oxygen and are therefore not thought to be particularly reactive. “From a pure chemistry point of view, this should be inert,” says Min.

To find out, Min and his colleagues studied the microparticles of a range of commonly used plastics – including polystyrene, polyethylene and polypropylene – and found that “water is a key player” in their effects.

They used techniques including fluorescence microscopy and electron spin resonance spectroscopy to show that a type of reactive oxygen species called hydroxyl radicals spontaneously forms at the surface between plastic and water, making the latter “not regular water anymore”, he says.

The team also showed that this effect is linked to electric charges forming at this plastic-water interface. These charges may help strip electrons from OH- ions in water, generating volatile hydroxyl radicals, says Min.

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In experiments, this electric charge attracted biological molecules such as DNA to the surface of microplastics when suspended in water, which appeared to damage both proteins and red blood cells.

The researchers also tested whether hydroxyl radicals were generated when the microparticles were suspended in serum from blood. The effect was weaker, but “still detectable”, says Min. Microplastics have been , however, signals of their presence throughout our bodies and false positive results.

If microplastics do enter our blood, laboratory studies have linked them to cellular , all of which can be caused by reactive oxygen species.

The findings could help explain how those molecules are being produced, says Min, although he adds that the potential size of the effect is unclear and other mechanisms could be involved. It may also depend on whether microplastics are disposed of by our bodies. “How much plastic is in a regular human being?” he says. “We have no idea right now.”

at the New Jersey Institute of Technology says the results are “very important”, and although they don’t directly answer how dangerous microplastics might be, they “provide a starting point” to help us understand the interaction between microplastics and cells.

at the University of New Mexico describes the results as a “critical building block” for this understanding. The surface area of microplastics is probably key to their effects, he says, pointing out that a half-centimetre ball of plastic could degrade into a quadrillion 50-nanometre microparticles, increasing its surface area 100,000 times.

That isn’t necessarily as worrying as it sounds, however. “I encourage people to take a deep breath,” says Campen.

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When the researchers added a surfactant – a chemical that weakens the forces holding the water molecules together – radical generation was dampened. Some lipids act as surfactants in the body. “Microplastics hit your lung and they are surrounded by surfactants immediately,” says Campen. “In most situations that I can imagine in a biological system, they will be surrounded by those lipids. The big concern is [whether] this is getting worse over time, and we really need to get a handle on what the health effects are, or could be, so that we can avoid exposures.”

The findings could also help scientists design safer materials, says Min. The researchers found that the most hydrophobic (water-repelling) plastics they tested, such as polyethylene and polypropylene, showed stronger radical-generating activity than more hydrophilic ones, such as PET (polyethylene terephthalate).

Campen notes, however, that the plastics with the lowest activity are also probably the ones that break down more slowly in the environment. “How do you make that trade off?”